* [patch, fortran] Fix PR 82567
@ 2017-10-18 0:52 Thomas Koenig
2017-10-18 1:42 ` Jerry DeLisle
0 siblings, 1 reply; 5+ messages in thread
From: Thomas Koenig @ 2017-10-18 0:52 UTC (permalink / raw)
To: fortran, gcc-patches
[-- Attachment #1: Type: text/plain, Size: 785 bytes --]
Hello world,
this patch fixes a regression with long compile times,
which came about due to our handling of array constructors
at compile time. This, togeteher with a simplification in
front end optimization, led to long compile times and large
code.
Regression-tested. OK for trunk and the other affected branches?
Regards
Thomas
2917-10-17 Thomas Koenig <tkoenig@gcc.gnu.org>
PR fortran/82567
* frontend-passes.c (combine_array_constructor): If an array
constructor is all constants and has more elements than a small
constant, don't convert a*[b,c] to [a*b,a*c] to reduce compilation
times.
2917-10-17 Thomas Koenig <tkoenig@gcc.gnu.org>
PR fortran/82567
* gfortran.dg/array_constructor_51.f90: New test.
[-- Attachment #2: array_constructor_51.f90 --]
[-- Type: text/x-fortran, Size: 450 bytes --]
! { dg-do compile }
! { dg-additional-options "-ffrontend-optimize -fdump-tree-original" }
! PR 82567 - long compile times caused by large constant constructors
! multiplied by variables
SUBROUTINE sub()
IMPLICIT NONE
INTEGER, PARAMETER :: n = 1000
REAL, ALLOCATABLE :: x(:)
REAL :: xc, h
INTEGER :: i
ALLOCATE( x(n) )
xc = 100.
h = xc/n
x = h*[(i,i=1,n)]
end
! { dg-final { scan-tree-dump-times "__var" 0 "original" } }
[-- Attachment #3: p1.diff --]
[-- Type: text/x-patch, Size: 1554 bytes --]
Index: frontend-passes.c
===================================================================
--- frontend-passes.c (Revision 253768)
+++ frontend-passes.c (Arbeitskopie)
@@ -1635,6 +1635,8 @@ combine_array_constructor (gfc_expr *e)
gfc_constructor *c, *new_c;
gfc_constructor_base oldbase, newbase;
bool scalar_first;
+ int n_elem;
+ bool all_const;
/* Array constructors have rank one. */
if (e->rank != 1)
@@ -1674,12 +1676,38 @@ combine_array_constructor (gfc_expr *e)
if (op2->ts.type == BT_CHARACTER)
return false;
- scalar = create_var (gfc_copy_expr (op2), "constr");
+ /* This might be an expanded constructor with very many constant values. If
+ we perform the operation here, we might end up with a long compile time,
+ so an arbitrary length bound is in order here. If the constructor
+ constains something which is not a constant, it did not come from an
+ expansion, so leave it alone. */
+#define CONSTR_LEN_MAX 42
+
oldbase = op1->value.constructor;
+
+ n_elem = 0;
+ all_const = true;
+ for (c = gfc_constructor_first (oldbase); c; c = gfc_constructor_next(c))
+ {
+ if (c->expr->expr_type != EXPR_CONSTANT)
+ {
+ all_const = false;
+ break;
+ }
+ n_elem += 1;
+ }
+
+ if (all_const && n_elem > CONSTR_LEN_MAX)
+ return false;
+
+#undef CONSTR_LEN_MAX
+
newbase = NULL;
e->expr_type = EXPR_ARRAY;
+ scalar = create_var (gfc_copy_expr (op2), "constr");
+
for (c = gfc_constructor_first (oldbase); c;
c = gfc_constructor_next (c))
{
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [patch, fortran] Fix PR 82567
2017-10-18 0:52 [patch, fortran] Fix PR 82567 Thomas Koenig
@ 2017-10-18 1:42 ` Jerry DeLisle
2017-10-18 2:09 ` Steve Kargl
0 siblings, 1 reply; 5+ messages in thread
From: Jerry DeLisle @ 2017-10-18 1:42 UTC (permalink / raw)
To: Thomas Koenig, fortran, gcc-patches
On 10/17/2017 03:36 PM, Thomas Koenig wrote:
> Hello world,
>
> this patch fixes a regression with long compile times,
> which came about due to our handling of array constructors
> at compile time. This, togeteher with a simplification in
> front end optimization, led to long compile times and large
> code.
>
> Regression-tested. OK for trunk and the other affected branches?
>
Well I know 42 is the answer to the ultimate question of the universe so this
must be OK. I just don't know what the question is.
OK and thanks,
Jerry
+#define CONSTR_LEN_MAX 42
+
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [patch, fortran] Fix PR 82567
2017-10-18 1:42 ` Jerry DeLisle
@ 2017-10-18 2:09 ` Steve Kargl
2017-10-18 12:03 ` Mikael Morin
2017-10-18 21:58 ` Thomas Koenig
0 siblings, 2 replies; 5+ messages in thread
From: Steve Kargl @ 2017-10-18 2:09 UTC (permalink / raw)
To: Jerry DeLisle; +Cc: Thomas Koenig, fortran, gcc-patches
On Tue, Oct 17, 2017 at 06:14:16PM -0700, Jerry DeLisle wrote:
> On 10/17/2017 03:36 PM, Thomas Koenig wrote:
> > Hello world,
> >
> > this patch fixes a regression with long compile times,
> > which came about due to our handling of array constructors
> > at compile time. This, togeteher with a simplification in
> > front end optimization, led to long compile times and large
> > code.
> >
> > Regression-tested. OK for trunk and the other affected branches?
> >
>
> Well I know 42 is the answer to the ultimate question of the universe so this
> must be OK. I just don't know what the question is.
>
> OK and thanks,
>
> Jerry
>
> +#define CONSTR_LEN_MAX 42
Actually, I was wondering about the choice myself. With
most common hardware having fairly robust L1 and L2 cache
sizes, a double precision array constructor with 42
elements only occupies 336 bytes. Seems small.
--
Steve
20170425 https://www.youtube.com/watch?v=VWUpyCsUKR4
20161221 https://www.youtube.com/watch?v=IbCHE-hONow
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [patch, fortran] Fix PR 82567
2017-10-18 2:09 ` Steve Kargl
@ 2017-10-18 12:03 ` Mikael Morin
2017-10-18 21:58 ` Thomas Koenig
1 sibling, 0 replies; 5+ messages in thread
From: Mikael Morin @ 2017-10-18 12:03 UTC (permalink / raw)
To: sgk, Jerry DeLisle; +Cc: Thomas Koenig, fortran, gcc-patches
Le 18/10/2017 à 04:05, Steve Kargl a écrit :
> On Tue, Oct 17, 2017 at 06:14:16PM -0700, Jerry DeLisle wrote:
>> On 10/17/2017 03:36 PM, Thomas Koenig wrote:
>>> Hello world,
>>>
>>> this patch fixes a regression with long compile times,
>>> which came about due to our handling of array constructors
>>> at compile time. This, togeteher with a simplification in
>>> front end optimization, led to long compile times and large
>>> code.
>>>
>>> Regression-tested. OK for trunk and the other affected branches?
>>>
>>
>> Well I know 42 is the answer to the ultimate question of the universe so this
>> must be OK. I just don't know what the question is.
>>
>> OK and thanks,
>>
>> Jerry
>>
>> +#define CONSTR_LEN_MAX 42
>
> Actually, I was wondering about the choice myself. With
> most common hardware having fairly robust L1 and L2 cache
> sizes, a double precision array constructor with 42
> elements only occupies 336 bytes. Seems small.
>
There is a -fmax-array-constructor=n option. Canât we use it for the limit?
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [patch, fortran] Fix PR 82567
2017-10-18 2:09 ` Steve Kargl
2017-10-18 12:03 ` Mikael Morin
@ 2017-10-18 21:58 ` Thomas Koenig
1 sibling, 0 replies; 5+ messages in thread
From: Thomas Koenig @ 2017-10-18 21:58 UTC (permalink / raw)
To: sgk, Jerry DeLisle; +Cc: fortran, gcc-patches
Hi Jerry and Steve,
>> Well I know 42 is the answer to the ultimate question of the universe so this
>> must be OK. I just don't know what the question is.
>>
>> OK and thanks,
>>
>> Jerry
>>
>> +#define CONSTR_LEN_MAX 42
> Actually, I was wondering about the choice myself. With
> most common hardware having fairly robust L1 and L2 cache
> sizes, a double precision array constructor with 42
> elements only occupies 336 bytes. Seems small.
Well, the answer is that I didn't know how to chose a reasonable
constant. I now actually ran some benchmarks using rdtsc, and
these seem to indicate that the optimum value for CONST_LEN_MAX
is actually quite short, 3 or 4, otherwise I just got a slowdown
or a break even.
So, I committed (r253872) with a length of 4 as a limit. If anybody
comes up with a better number, we can always change this.
So, thanks for the review and the comments.
Regards
Thomas
If somebody wants to check, here is the test case:
main.f90:
module tick
interface
function rdtsc()
integer(kind=8) :: rdtsc
end function rdtsc
end interface
end module tick
program main
use tick
use tst
implicit none
integer(8) :: t1, t2
t1 = rdtsc()
call sub1(2.0)
t2 = rdtsc()
! print *,"sub1 : ", t2-t1
t1 = rdtsc()
do i=1,10000
call sub1(2.0)
end do
t2 = rdtsc()
print *,"sub1 : ", t2-t1
t1 = rdtsc()
do i=1,10000
call sub2(2.0)
end do
t2 = rdtsc()
print *,"sub2 : ", t2-t1
end program main
tst.f90:
module tst
integer, parameter :: n=4
real, dimension(n) :: x
real, dimension(n), parameter :: s = [(i,i=1,n)]
contains
subroutine sub1(a)
real, intent(in) :: a
x(1) = a * 1.0
x(2) = a * 2.0
x(3) = a * 3.0
x(4) = a * 3.0
end subroutine sub1
subroutine sub2(a)
x(:) = a * s(:)
end subroutine sub2
end module tst
rdtsc.s:
.file "rdtsc.s"
.text
.globl rdtsc_
.type rdtsc_, @function
rdtsc_:
.LFB0:
.cfi_startproc
rdtsc
shl $32, %rdx
or %rdx, %rax
ret
.cfi_endproc
.LFE0:
.size rdtsc_, .-rdtsc_
.section .note.GNU-stack,"",@progbits
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2017-10-18 0:52 [patch, fortran] Fix PR 82567 Thomas Koenig
2017-10-18 1:42 ` Jerry DeLisle
2017-10-18 2:09 ` Steve Kargl
2017-10-18 12:03 ` Mikael Morin
2017-10-18 21:58 ` Thomas Koenig
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